1. Field of the Invention
The present invention relates generally to semiconductor memory devices, and more particularly, to a semiconductor memory device having an associative function which can be used for retrieving information based on an input of a keyword and an operand data pair producing mechanism in a data flow computer.
2. Description of the Related Art
Conventionally, as a semiconductor memory device having an associative function has been known as disclosed in, for example, Technical Report of Institute of Electronic and Communication Engineers of Japan, (1983) SSD83-78, pp. 45-52. The semiconductor memory device is a so-called logic-in memory including a plurality of memory cells where each cell has a collating and comparing circuit. In the logic-in memory of the above described document, all of the memory cells determine the collation. Thus, the logic-in memory is referred to as a full-associative memory. The full-associative memory includes a memory cell array having a plurality of memory cells arranged in a matrix of rows and columns. In the full-associative memory, all of the memory cells have a function for determining the collation, so that retrieval along a word direction (row direction) in the memory cell array and retrieval along a bit direction (column direction) therein are performed based on an input of a keyword. More specifically, a complete determination of the collation along the word direction and the bit direction is made.
In the full-associative memory, a complete determination of the collation can be made while the area of a unit memory cell is increased. Therefore, the area of the full-associative memory illustrated in the above described document is increased by approximately six times the area of a general-purpose dynamic memory having the same storage capacity as the area of the full-associative memory.
Additionally, if and when a complete determination of the collation is not required, that is, when a partial determination of the collation or a determination of the collation depending on the condition is made, it becomes redundant to have comparing logical circuits for a determination of the collation, respectively, in all of the memory cells. Therefore, it is not economical to use a full-associative memory, in a semiconductor device.